Hey I've just finished AS doing almost the same subjects as you just swapping maths for geography
Most people I know have a ringbinder per subject and write on refill pads, you get a lot of handouts in sixth form especially for sciency projects, just keeps all your notes in one place with the worksheets etc. If you don't get your textboooks given to you you need to ask about the exam board and which course you are on (some have multiple) for each subject so you can buy their textbook and I would also recommend a revision guide at the same time, saves buying it when the demand gets high around exam time!
We have to wear smart all the time at my sixth form (it's part of a school so that's probably why) and a lot of guys get suits and jackets from Topman, designer outlets are good for clothes, most high street shops will sell fashionable clothes for whatever you're allowed to wear. ASOS is also very good! I recommend buying a decent bag also because those folders and textbooks can get seriously heavy and tricky to carry :P
NUS card is good because it gives you discounts actually instore in places like Topman, New Look, etc as well as online. It's £12 a year which really isn't that bad if you do most of your shopping instore. If you don't and do most of it online then you get pretty much the same discounts on UniDays providing you have a college email address, and it's free.
Don't really know what enrolment day is, I never had one of those or an induction day, but I imagine on induction day you find out your timetable, meet people you'll be in a class with etc
Expenditure depends whether you have a canteen or something, everyone at my school has the school lunch which their parents pay for on a parentpay thing online and we scan our thumbprints as we walk in and money gets taken out of the account, any other money is spent going into town to the local shops to buy sweets and drinks etc